Friction clutch



April 8, 1947. G. F. DRAKE 2,418,466

FRICTION CLUTCH Filed Feb. 28, 1944 van Patentecl Ap 8, A1947 FRICTION 'CLUTCH `Gfeorgfe :Forrest Drake, Rockford,` Ill.lassgnor :to fwoodwardf Governor Company, Rockford, Ill., :afcorporation ofIllinois Application February 28, i19M,Serial 'NoL 4524,72100 41Claims. 1 "One object of this *invention lis to provide a novelfriction clutch whose Vtorque 4transmitting Vcapacity isi substantially unaffected Iby lubrication ofit's gripping surfaces.

Amoredetailed object is 4to provide a friction clutch :in which the coacting gripping elements are so constructed Aand pressed together as to break down any lubricant film on the co-acting '.surfacesiand causelthesurfaces to gripeach other with a friction coeicient approximating that of the surfaceswhendry.

Another object is to provide a novelly arranged electromagnetic actuator for causing gripping eny f'gagementof the clutch-elements.

^Other objects land advantages of the invention iwill become apparent from ithe' Yfollowing detailed v=lde'scriptiontaken-in connection with the accomy fpanying drawings-in -Which @Figure `1` i-s-a-diametricall-sectional -viewof the improved clutchrand-associated gearing.

Fig. 2 is a face view of one of the clutch elefments'taken along the lineV 2-"2 of Fig. 1.

iFig.- 3 is anenlarged Afragmentary section of a portion of Fig. 1.

The clutch shown for purposes of illustration comprises two rotary elements in the form of disks 3 and 4 presenting smooth and continuous gripping surfaces 5 and 6 composed of nonporous material which is incapable of absorbing ordinary lubricants. While resins, various metals, and other non-absorbent materials may be used, the surfaces are formed of hardened steel in the present instance in order to possess high resistance to Wear. The surface 5 is the flat end face of the disk 3 whose hub I is pressed onto a bushing 8 and into the inner race 9 of an antifriction thrust bearing Ill which is supported in a cross member II of a casing I2 which houses the clutch and associated gearing. A gear I3 also fast on the bushing 8 is driven from a pinion I4, the two gears being lubricated by oil or grease contained within the casing.

The face 6 is flat and formed on the end of an annular rib I5 projecting axially from the disk 4 toward the disk 3. This rib is of narrow radial width and of substantially the full diameter of the disk so as to provide a moment arm of maximum radius and yet possess a comparatively small total area. Herein the, disk 4 is fast on a bushing I6 carrying a pinion I'I which meshes with a gear I8 to form another step in the lubricated speed reduction gearing.

Herein, selective engagement and disengagement of the clutch are controlled by an electromagnet I9 stationarily mounted in the casing I2 .2 andhaving concentric' axi'allyifacing poies:20.f.and l2-I Whichattract an -armatureidiskL22 upon ener- `gization of a winding 123. .The Varmatureisast` Von a 'shaft l2-4 -journaled in the ibushing .and projecting Jthroughthe Lbushing :.I'B and thepinion ft?. -At V:its flower-lend, `Athel shaft `carries 2a.nut

lwhich` limits fthe F.motion i of fthearmature ltoward lithe lmagnetfpoles so las-tto leave `a narrow;air I`:gap 22T-Ia A:of ra few mthousandthspf ian: inch and .iprevent actual Contact between thelarmature i and magnet-when ther-latter .isaenergized By .fem- `rployingiclutch surfaces of `rigid material "such las Yhardened .steel, the gap is i maintained through long` periods.` of Lservice :use `andzwear on :the-magnetic parts isiavoide'd. Themass `of` the rotating vparts is minimized :by Jmounting fthe magnet -stationarily.

``When-the magnet is 'deenergizedv oilorgrease -contained within lthe casing I 2 to. providedubricant ifor ,ther gearing andA associated i parts-will Vwork tonto and `between the gripping surfaces @Band but will `not be absorbed by thedatter -owing totheir smooth` and `non-porous character.

Therefore, when the surfaces are drawn together under the force of the magnet, the lubricant will be squeezed out from between the surfaces, and the lm which tends to remain on these surfaces will be broken down if the unit pressure is sufilciently high and is correlated with the shape and other characteristics of the gripping surfaces and the character of the lubricant employed. For example, if, in the arrangement above described, the rib I5 is made has inches in diameterI with a face substantially 11e of an inch wide, ordinary lubricants will be excluded from the gripping area effectively under a total magnet force of 50 pounds, this being 230 pounds per square inch over the area 6. It has been found that the clutch thus constructed will exert, without slipping, a torque of 5 pound inches as compared to a torque of 5% pound inches when the clutch is engaged with the surfaces dry. Thus, the film of oil existing between the coacting gripping faces 5 and 6 is broken down and squeezed out of the narrow gripping area so completely that the surface possess an effective coefcient of friction very closely approximating that of the surfaces when the latter are dry or unlubricated. Relative motion between the clutch parts assists in breaking down the oil film and facilitates the attainment of optimum torque transmitting capacity.

I claim as my invention:

1. A friction clutch adapted to operate in a lubricant comprising, a rotary driving element, a rotary driven element supported for axial movement relative thereto, said elements having axially engageable annular surfaces near the periphery thereof of narrow radial width and composed of hardened steel, each of said surfaces being smooth and circumferentially continuous, and means by which said elements may be urged into gripping engagement under a unit pressure on said surfaces of sufficient magnitude to squeeze out said lubricant so completely that the coeiicient of friction between the surfaces is increased to a value approximating that of the surfaces when the latter are dry, the narrow width of said annular surfaces enabling rapid ejection of the lubricant therefrom upon actuation of said urging means.

2. A friction clutch comprising, a rotary diiv` correlated with the size, shape, and physical characteristics of said surfaces and of suiicient magnitude to squeeze lubricant out of said area so completely that the coefcient of frictionbetween said surfaces is increased to a value substantially equal to that of the surfaces when the latter are dry, the narrow width of said annular surfaces enabling rapid' ejection of the lubricant therefrom upon actuation of Lsaid urging means.

3. A friction cltuch for transmitting power even when bathed in lubricant comprising a rotary driving element, a rotary driven element coaxially mounted with respect thereto, said elements havingannular coacting surfaces near the periphery thereof which are smooth and continuous and incapable of absorbing said lubricant, and selectively controllable means for urging said elements into gripping engagement under a force correlated with the size, shape, and characteristics of said surfaces and of sufficient magnitude to break down substantially completely the lubricant lm tending to separate the surfaces, said coacting surfaces being sufficiently narrow in radial width as to enable rapid and positive ejection of said lubricant upon actuation of said urging means. y

A4. A friction clutch for transmittingvtorque in the presence of a lubricant comprising a rotary driving element, a rotary driven element, said elements being arranged coaxially and presenting unbroken annular coacting surfaces near the outer periphery thereof adapted for gripping engagement and incapable of absorbing lubricant to vwhich the surfaces may be exposed, and selec-- tively controllable means for applying a unit pressure on said coacting surfaces in excess of the film strength of ordinary oil lubricants to force said elements into gripping engagement, said coacting annular surfaces being of a suciently narrow width as not only to promote the development of said excessive unit pressure but also to enable rapid ejection of oil therefrom under conditions of rapidly repetitive clutching.

GEORGE FORREST DRAKE.

REFERENCES CITED y UNITED STATES PATENTS Number Name Y Date 1,866,128 Pfeiffer 1---" July 5, 1932 1,610,141 Michael Dec. 7, 1926 1,500,971 Wallace July 8, 1924 1,963,638 Wilsing June 19, 1934 1,189,176 Price June 27, 1916 987,954 Brush Mar. 28,'1911 FOREIGN PATENTS Number Country Date 319,852 British Oct. 3, 1929 

